Reading integer input in Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Java code reading an integer?

Consider the following Java program that reads an integer from the user and prints it doubled. What will be printed if the user inputs 7?

Java

import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int num = scanner.nextInt();
        System.out.println(num * 2);
    }
}

A 0

B 7

C Error: InputMismatchException

D 14

💡 Hint

Remember that nextInt() reads an integer and you multiply it by 2 before printing.

The program reads the integer 7, then multiplies it by 2, printing 14.

❓ Predict Output

intermediate

What happens if non-integer input is given?

What will happen if the user inputs abc when running this Java code?

Java

import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int num = scanner.nextInt();
        System.out.println(num);
    }
}

A Program waits forever

B Throws InputMismatchException

C Prints 0

D Prints abc

💡 Hint

nextInt() expects an integer input.

If the input is not an integer, nextInt() throws InputMismatchException.

🧠 Conceptual

advanced

Which Scanner method reads an integer from input?

You want to read an integer value from the user in Java. Which Scanner method should you use?

A nextInt()

B nextDouble()

C nextLine()

D next()

💡 Hint

Think about which method returns an int type.

nextInt() reads the next token as an integer value.

📝 Syntax

advanced

Identify the syntax error in this integer input code

Which option contains a syntax error when trying to read an integer from input?

Java

import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int num = scanner.nextInt()
        System.out.println(num);
    }
}

A Scanner class not imported

B Using nextLine() instead of nextInt()

C Missing semicolon after scanner.nextInt()

D Variable num declared as String

💡 Hint

Check punctuation at the end of statements.

The line 'int num = scanner.nextInt()' is missing a semicolon at the end.

🚀 Application

expert

What is the value of 'sum' after reading two integers?

This Java program reads two integers from the user and sums them. If the user inputs 3 and then 5, what is the value of the variable sum after execution?

Java

import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int a = scanner.nextInt();
        int b = scanner.nextInt();
        int sum = a + b;
        System.out.println(sum);
    }
}

A 8

B 35

C Error: InputMismatchException

D 0

💡 Hint

Sum means adding the two numbers, not concatenating.

The program reads 3 and 5 as integers, sums them to 8, and prints 8.